OBJECTIVE:: To evaluate HIV-1 transmission trends and the impact of highly active antiretroviral therapy (HAART) on newly diagnosed HIV infections in Geneva, Switzerland. DESIGN:: Retrospective molecular epidemiology analysis of all newly HIV-diagnosed individuals between 2008 and 2010. METHODS:: Phylogenetic analyses were performed using pol sequences of 780 newly HIV-1 diagnosed individuals between 2000 and 2010 (mandatory reporting) and 1058 individuals diagnosed before 2000. All clusters (bootstrap value >98%) including individuals diagnosed in 2008-2010 were analyzed. Recent HIV infections (<1 year) were determined by documented seroconversion and/or fraction of ambiguous nucleotides. Median viral load and HAART coverage during the study period were obtained from patients included in the Swiss HIV Cohort Study (SHCS). RESULTS:: Among 142 newly diagnosed individuals during 2008-2010, 49% had a recent infection and 42% were included in transmission clusters. Among the latter, two-thirds were included in new clusters and one-third expanded previously known clusters. MSM carrying resistant strains were more frequently included in clusters. Only 1.8% of individuals diagnosed before 2000 and 10.8% diagnosed during 2000-2008 were included in clusters involving individuals diagnosed between 2008 and 2010. During 2008-2010, the median population viral load of SHCS-enrolled individuals was significantly lower for individuals diagnosed before 2000 than for those diagnosed during 2000-2008 and 2008-2010 and HAART coverage significantly higher. CONCLUSIONS:: MSM with recent HIV infection are a significant source of onward transmission. Individuals diagnosed before 2000 were only exceptionally related to newly diagnosed infections between 2008 and 2010. Prevention campaigns need to be focused on improving diagnosis for recently infected individuals.

aLaboratory of Virology, Department of Genetics and Laboratory Medicine, University Hospital bHIV Unit, Division of Infectious Diseases, Department of Medical Specialities, University Hospital cComputational Evolutionary Genomics Group, University of Geneva Hospitals and School of Medicine, Geneva, Switzerland.